Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.58   7.697%   $224.6344   $224.63   $224.65   $224.60  
  Purchase #2 $52.53   10.863%   $58.2363   $58.24   $58.25   $58.20  
  Purchase #3 $109.54   5.266%   $115.3084   $115.31   $115.30   $115.30  
  Purchase #4 $225.90   6.825%   $241.3177   $241.32   $241.30   $241.30  
  Purchase #5 $22.29   12.820%   $25.1476   $25.15   $25.15   $25.10  
  Purchase #6 $190.40   12.793%   $214.7579   $214.76   $214.75   $214.80  
  Purchase #7 $126.89   12.851%   $143.1966   $143.20   $143.20   $143.20  
  7 purchase totals = $936.13       $1,022.5989   $1,022.61   $1,022.60   $1,022.50